Posted by bellefy@gmail.com on 05/19/06 21:07

Hi All,

I have a question about a formula I found online at
http://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2.

To determine if an integer is a power of 2, the author states that:

f = (v & (v -1)) == 0;

I am very proficient with scripting techniques using PHP so I
understand what we're trying to accomplish here.

However, I can't seem to figure out how to make the example work... :-(

Take, for example, 16.

f = (16 & (16 - 1)) == 0;
f = (16 & (15)) == 0;

The test is always false????????

I think I am not understanding the steps completely...

For reference, in PHP, there is no operator &. The logical AND operator
is &&.

In PHP, the same formula would be written as:

if((v && (v-1)) == 0){
return true;
}

Can anyone explain this to me? I would greatly appreciate any help.

Thanks in advance,

Tim Bellefy

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